Oriented polyethylene films and articles comprising the same

The present invention relates to oriented, multilayer polyethylene films, to laminates comprising such films, and to articles comprising such films and laminates.

As global interest solidifies in reducing packaging waste and making flexible packaging more sustainable, there is an increasing amount of effort to develop materials and technologies that would enhance the sustainability of flexible packaging. Flexible packaging film structures are often formed of multiple types of polymeric materials including, for example, polyethylene, polypropylene, ethylene vinyl alcohol, polyethylene terephthalate, polyamide and others. Such materials are typically combined to achieve a balance of properties that are beyond the reach of a single material type. However, due to the dissimilarity of these materials, the final package is typically not easy to recycle. Thus, there is also a movement towards single component structures (e.g., all polyethylene structures) to improve the recyclability profile. In the case of all polyethylene structures, for example, certain performance metrics (e.g., mechanical properties) will need to be enhanced to maintain the level of performance expected of these structures when formed from different polymeric materials, while improving recyclability. Thus, new resin and processing technologies will be needed to bridge performance deficiencies of polyethylene relative to other material types.

One such relatively new material technology on the processing side is biaxially oriented polyethylene (BOPE) films. Such BOPE films are formed by cast extrusion, and are then oriented in the machine direction (MD) followed by orientation in the transverse direction (TD) in a tenter frame. Alternatively, this process can be performed simultaneously. Due to the molecular architecture, microstructure and crystallization kinetics of polyethylene, it is often difficult to biaxially orient conventional polyethylene.

It would be desirable to have new polyethylene-based compositions that have good processability into biaxially oriented polyethylene films as well as new biaxially oriented polyethylene films having desired and/or improved properties. It would also be desirable to have new polyethylene-based compositions that have good processability into uniaxially oriented (e.g., machine direction oriented) polyethylene films as well as new uniaxially oriented polyethylene films having desired and/or improved properties.

The present invention provides polyethylene-based compositions suitable for processing into biaxially oriented, multilayer polyethylene films, as well as biaxially oriented, multilayer polyethylene films having desired and/or improved properties. Such polyethylene-based compositions, in some embodiments, can advantageously expand the operating window for stretching films to provide biaxially oriented polyethylene films. For example, by expanding the operating window for biaxial orientation, higher density polyethylenes can be oriented which can lead to improved film stiffness. Other advantages can include, without limitation, better conversion and printability of films, improved optics (e.g., higher clarity and lower haze), improved barrier performance for metallized biaxially oriented polyethylene films, and improved processability on larger, wider tenter frames. The present invention also provides polyethylene-based compositions suitable for processing into uniaxially oriented (e.g., machine direction oriented), multilayer polyethylene films, as well as uniaxially oriented, multilayer polyethylene films having desired and/or improved properties.

In one aspect, a biaxially oriented, multilayer polyethylene film comprises at least one inner layer comprising:

In another aspect, the present invention relates to articles, such as food packages. In one aspect, an article comprises any of the biaxially oriented, multilayer polyethylene films disclosed herein.

In another aspect, the present invention relates to laminates and articles formed from such laminates. In some embodiments, a laminate comprises a first film comprising a polyethylene-based sealant film, polyethylene terephthalate, polypropylene, or polyamide; and a biaxially oriented, multilayer polyethylene film according to any of the embodiments disclosed herein, wherein the first film is laminated to the multilayer polyethylene film. In one aspect, an article comprises any of the laminates disclosed herein.

These and other embodiments are described in more detail in the Detailed Description.

Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percents are based on weight, all temperatures are in ° C., and all test methods are current as of the filing date of this disclosure.

The term “composition,” as used herein, refers to a mixture of materials which comprises the composition, as well as reaction products and decomposition products formed from the materials of the composition.

“Polymer” means a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term homopolymer as defined hereafter, and the term interpolymer as defined hereinafter. Trace amounts of impurities (for example, catalyst residues) may be incorporated into and/or within the polymer. A polymer may be a single polymer, a polymer blend or a polymer mixture, including mixtures of polymers that are formed in situ during polymerization.

The term “homopolymer,” as used herein, refers to polymers prepared from only one type of monomer with the understanding that trace amounts of impurities can be incorporated into the polymer structure.

The term “interpolymer,” as used herein, refers to polymers prepared by the polymerization of at least two different types of monomers. The generic term interpolymer thus includes copolymers (employed to refer to polymers prepared from two different types of monomers), and polymers prepared from more than two different types of monomers.

The terms “olefin-based polymer” or “polyolefin”, as used herein, refer to a polymer that comprises, in polymerized form, a majority amount of olefin monomer, for example ethylene or propylene (based on the weight of the polymer), and optionally may comprise one or more comonomers.

The term, “ethylene/α-olefin interpolymer,” as used herein, refers to an interpolymer that comprises, in polymerized form, a majority amount (>50 mol %) of units derived from ethylene monomer, and the remaining units derived from one or more α-olefins. Typical α-olefins used in forming ethylene/α-olefin interpolymers are C-Calkenes.

The term, “ethylene/α-olefin copolymer,” as used herein, refers to a copolymer that comprises, in polymerized form, a majority amount (>50 mol %) of ethylene monomer, and an α-olefin, as the only two monomer types.

The term “α-olefin”, as used herein, refers to an alkene having a double bond at the primary or alpha (α) position.

“Polyethylene” or “ethylene-based polymer” shall mean polymers comprising a majority amount (>50 mol %) of units which have been derived from ethylene monomer. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include Low Density Polyethylene (LDPE); Linear Low Density Polyethylene (LLDPE); Ultra Low Density Polyethylene (ULDPE); Very Low Density Polyethylene (VLDPE); single-site catalyzed Linear Low Density Polyethylene, including both linear and substantially linear low density resins (m-LLDPE); ethylene-based plastomers (POP) and ethylene-based elastomers (POE); Medium Density Polyethylene (MDPE); and High Density Polyethylene (HDPE). These polyethylene materials are generally known in the art; however, the following descriptions may be helpful in understanding the differences between some of these different polyethylene resins.

The term “LDPE” may also be referred to as “high pressure ethylene polymer” or “highly branched polyethylene” and is defined to mean that the polymer is partly or entirely homo-polymerized or copolymerized in autoclave or tubular reactors at pressures above 14,500 psi (100 MPa) with the use of free-radical initiators, such as peroxides (see for example U.S. Pat. No. 4,599,392, which is hereby incorporated by reference). LDPE resins typically have a density in the range of 0.916 to 0.935 g/cm.

The term “LLDPE”, includes both resin made using the traditional Ziegler-Natta catalyst systems and chromium-based catalyst systems as well as single-site catalysts, including, but not limited to, substituted mono- or bis-cyclopentadienyl catalysts (typically referred to as metallocene), constrained geometry catalysts, phosphinimine catalysts & polyvalent aryloxyether catalysts (typically referred to as bisphenyl phenoxy), and includes linear, substantially linear or heterogeneous polyethylene copolymers or homopolymers. LLDPEs contain less long chain branching than LDPEs and includes the substantially linear ethylene polymers which are further defined in U.S. Pat. Nos. 5,272,236, 5,278,272, 5,582,923 and 5,733,155; the homogeneously branched linear ethylene polymer compositions such as those in U.S. Pat. No. 3,645,992; the heterogeneously branched ethylene polymers such as those prepared according to the process disclosed in U.S. Pat. No. 4,076,698; and/or blends thereof (such as those disclosed in U.S. Pat. Nos. 3,914,342 or 5,854,045). The LLDPEs can be made via gas-phase, solution-phase or slurry polymerization or any combination thereof, using any type of reactor or reactor configuration known in the art.

The term “MDPE” refers to polyethylenes having densities from 0.926 to 0.935 g/cm. “MDPE” is typically made using chromium or Ziegler-Natta catalysts or using single-site catalysts including, but not limited to, substituted mono- or bis-cyclopentadienyl catalysts (typically referred to as metallocene), constrained geometry catalysts, phosphinimine catalysts & polyvalent aryloxyether catalysts (typically referred to as bisphenyl phenoxy), and typically have a molecular weight distribution (“MWD”) greater than 2.5.

The term “HDPE” refers to polyethylenes having densities greater than about 0.935 g/cmand up to about 0.980 g/cm, which are generally prepared with Ziegler-Natta catalysts, chrome catalysts or single-site catalysts including, but not limited to, substituted mono-or bis-cyclopentadienyl catalysts (typically referred to as metallocene), constrained geometry catalysts, phosphinimine catalysts & polyvalent aryloxyether catalysts (typically referred to as bisphenyl phenoxy).

The term “ULDPE” refers to polyethylenes having densities of 0.855 to 0.912 g/cm, which are generally prepared with Ziegler-Natta catalysts, chrome catalysts, or single-site catalysts including, but not limited to, substituted mono-or bis-cyclopentadienyl catalysts (typically referred to as metallocene), constrained geometry catalysts, phosphinimine catalysts & polyvalent aryloxyether catalysts (typically referred to as bisphenyl phenoxy). ULDPEs include, but are not limited to, polyethylene (ethylene-based) plastomers and polyethylene (ethylene-based) elastomers. Polyethylene (ethylene-based) elastomers plastomers generally have densities of 0.855 to 0.912 g/cm.

“Blend”, “polymer blend” and like terms mean a composition of two or more polymers. Such a blend may or may not be miscible. Such a blend may or may not be phase separated. Such a blend may or may not contain one or more domain configurations, as determined from transmission electron spectroscopy, light scattering, x-ray scattering, and any other method known in the art. Blends are not laminates, but one or more layers of a laminate may contain a blend. Such blends can be prepared as dry blends, formed in situ (e.g., in a reactor), melt blends, or using other techniques known to those of skill in the art.

All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of “up to 25 wt. %, or, more specifically, 5 wt. % to 20 wt. %”, are inclusive of the endpoints and all intermediate values of the ranges of “5 wt. % to 25 wt. %,” etc.). Moreover, stated upper and lower limits can be combined to form ranges (e.g. “at least 1 or at least 2 weight percent” and “up to 10 or 5 weight percent” can be combined as the ranges “1 to 10 weight percent”, or “1 to 5 weight percent” or “2 to 10 weight percent” or “2 to 5 weight percent”).

The terms “comprising,” “including,” “having,” and their derivatives, are not intended to exclude the presence of any additional component, step or procedure, whether or not the same is specifically disclosed. In order to avoid any doubt, all compositions claimed through use of the term “comprising” may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless stated to the contrary. In contrast, the term, “consisting essentially of” excludes from the scope of any succeeding recitation any other component, step or procedure, excepting those that are not essential to operability. The term “consisting of” excludes any component, step or procedure not specifically delineated or listed.

The present invention generally relates to oriented, multilayer polyethylene films. In some embodiments, such films are biaxially oriented. Such films are biaxially oriented using a tenter frame in some embodiments. In some embodiments, such films are uniaxially oriented in the machine direction. The oriented, multilayer polyethylene films utilize in at least one inner layer a polyethylene-based composition that can advantageously expand the operating window for stretching the films. For example, by expanding the operating window for biaxial orientation, higher density polyethylenes can be oriented which can lead to improved film stiffness. The oriented, multilayer polyethylene films, in some embodiments, can be used in packaging applications.

In one aspect, a biaxially oriented, multilayer polyethylene film comprises at least one inner layer comprising:

wherein R1-R5 comprise the same or different moieties chosen from hydrogen and a C-Calkyl. In some embodiments, the polyethylene-based composition comprises 20 to 2000 ppm of the sorbitol acetal derivative based on the total weight of the polyethylene-based composition.

In some embodiments, the biaxially oriented film is oriented in the machine direction at a draw ratio from 2:1 to 9:1 and in the cross direction at a draw ratio from 2:1 to 11:1. The biaxially oriented film, in some embodiments, is oriented in the machine direction at a draw ratio from 2:1 to 6:1 and in the cross direction at a draw ratio from 2:1 to 9:1. In some embodiments, the biaxially oriented film is oriented in the machine direction at a draw ratio from 4:1 to 6:1 and in the cross direction at a draw ratio from 6:1 to 9:1.

In some embodiments, the biaxially oriented, multilayer polyethylene film further comprises a second polyethylene composition, wherein the second polyethylene composition exhibits at least two local peaks, excluding the soluble fraction, in comonomer distribution measured by crystallization elution fractionation, wherein one of the peaks is between 40° C. and 95° C. The second polyethylene composition, in some embodiments, exhibits at least two local peaks, excluding the soluble fraction, in comonomer distribution measured by crystallization elution fractionation, wherein one of the peaks is between 40° C. and 90° C. In some embodiments, the second polyethylene composition exhibits at least two local peaks, excluding the soluble fraction, in comonomer distribution measured by crystallization elution fractionation, wherein one of the peaks is between 40° C. and 87° C. The second polyethylene composition in some embodiments has a density from 0.928 to 0.940 g/cm. In some embodiments, the inner layer comprising the polyethylene-based composition further comprises the second polyethylene composition.

In some embodiments, the overall density of the biaxially oriented, multilayer film is from 0.931 to 0.975 g/cm.

In some embodiments, the biaxially oriented, multilayer film has a thickness of 5 to 50 microns.

The biaxially oriented, multilayer film, some embodiments, further comprises a layer that comprises polyamide or ethylene vinyl alcohol.

In some embodiments, the biaxially oriented, multilayer film further comprises an outer layer that is a sealant layer.

In some embodiments, the biaxially oriented, multilayer film further comprises a layer comprising a metal deposited on an outer layer of the film, wherein the metal comprises Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn, Si, Mg, or oxides thereof.

In another aspect, the present invention relates to articles, such as food packages. In one aspect, an article comprises any of the inventive biaxially oriented, multilayer polyethylene films disclosed herein.

In another aspect, the present invention relates to laminates and articles formed from such laminates. In some embodiments, a laminate comprises a first film comprising a polyethylene-based sealant film, polyethylene terephthalate, polypropylene, or polyamide; and a biaxially oriented, multilayer polyethylene film according to any of the embodiments disclosed herein, wherein the first film is laminated to the multilayer polyethylene film. In one aspect, an article comprises any of the laminates disclosed herein.

In another aspect, the present invention relates to a uniaxially oriented, multilayer polyethylene film that comprises:

wherein R1-R5 comprise the same or different moieties chosen from hydrogen and a C-Calkyl. In some embodiments, the film is oriented in the machine direction.

In some embodiments, the uniaxially oriented film is oriented in the machine direction at a draw ratio from 2:1 to 9:1. The uniaxially oriented film, in some embodiments, is oriented in the machine direction at a draw ratio from 2:1 to 6:1. In some embodiments, the uniaxially oriented film is oriented in the machine direction at a draw ratio from 4:1 to 6:1.

In some embodiments, the uniaxially oriented, multilayer polyethylene film further comprises a second polyethylene composition, wherein the second polyethylene composition exhibits at least two local peaks, excluding the soluble fraction, in comonomer distribution measured by crystallization elution fractionation, wherein one of the peaks is between 40° C. and 95° C. The second polyethylene composition, in some embodiments, exhibits at least two local peaks, excluding the soluble fraction, in comonomer distribution measured by crystallization elution fractionation, wherein one of the peaks is between 40° C. and 90° C. In some embodiments, the second polyethylene composition exhibits at least two local peaks, excluding the soluble fraction, in comonomer distribution measured by crystallization elution fractionation, wherein one of the peaks is between 40° C. and 87° C. The second polyethylene composition in some embodiments has a density from 0.928 to 0.940 g/cm. In some embodiments, the inner layer comprising the polyethylene-based composition further comprises the second polyethylene composition.

In some embodiments, the overall density of the uniaxially oriented, multilayer film is from 0.931 to 0.975 g/cm.

In some embodiments, the uniaxially oriented, multilayer film has a thickness of 5 to 50 microns.

The uniaxially oriented, multilayer film, some embodiments, further comprises a layer that comprises polyamide or ethylene vinyl alcohol.

In some embodiments, the uniaxially oriented, multilayer film further comprises an outer layer that is a sealant layer.

In some embodiments, the uniaxially oriented, multilayer film further comprises a layer comprising a metal deposited on an outer layer of the film, wherein the metal comprises Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn, Si, Mg, or oxides thereof.

In another aspect, the present invention relates to articles, such as food packages. In one aspect, an article comprises any of the inventive uniaxially oriented, multilayer polyethylene films disclosed herein.